The temperature also affects the resistance dramatically. This is because when a wire is heated, the fixed atoms inside the wire vibrate more violently. This means that the free electrons will collide more as there is a smaller inter-atomic distance for the free electrons to pass through. The diagram below shows this.
The length of the wire is a huge factor. It is so important because the free electrons carry the charge and if there were a large distance, it would take a long period of time for the free electrons to travel from one side to another. The longer it takes for the free electrons to travel, the smaller the current would be. This would mean that resistance is greater. Below shows an example.
The diagram shows that the resistance of wire X is half of the resistance of wire Y. This is because the free electrons in wire X only has to travel N whereas the free electrons in wire Y has to travel 2N which is exactly twice as long. As it has to travel twice the distance, it would take twice the time, which would double resistance. This shows me that length is directly proportional to resistance and I aim to prove this in this investigation. I predict that when I collect my results, it will prove to me that the length of the wire is directly proportional to resistance.
All four of the factors can dramatically alter resistance and if I could I would conduct many experiments to prove all of these but unfortunately, I do not have the time or the equipment to do so. I will only conduct one experiment and this will be on the length of the wire.
Safety
To ensure safety, I will keep all liquids at a fair distance from my equipment, as water is a very good conductor of electricity. I will also remove all metallic jewellery such as watches and other metal substances my classmates, or I am in contact with. This is important and must not be forgotten because a flow of current comes into contact with one’s watch; it will travel into the body causing massive damage. There are many other safety precautions which also must not be forgotten. These safety precautions include tucking in chairs, tucking in shirts, keeping all fire exits clear and tying hair back. Even though a fire is extremely unlikely and almost impossible, it should still be carried out. These must all be carried out or there will be a tremendous risk of pupils suffering from accidents.
Fair test
To ensure my test is fair, I will take immense care in my actions and I will make sure nobody will tamper with my equipment. I will measure my wires many times to ensure I have made no error. I will use the millimetre unit to measure, as I believe this will increase accuracy. In such an investigation, accuracy is key. I will also take immense care to make sure the potential difference remains constant throughout my investigation as potential difference can alter electrical resistance dramatically. I plan to use a potential difference of 2v. I chose 2v because it is high enough to see clearly how it affects electrical resistance but it is not so much that it would heat up the wire. As I stated earlier, the temperature of the wire can also alter the electrical resistance so I must not heat up the wire or this could again decrease the accuracy of my results. I will take tremendous care to ensure that the crocodile clips clip the wire at exactly the point I want. I will check this many times because if the crocodile clip is clipped too far, the resistance would be too high. As I stated earlier, the longer a wire is, the greater the resistance will be. So if I placed a crocodile clip
List of Equipment
To complete this investigation, a lot of equipment will be required. The equipment and the reason for using them are listed below.
-
Voltmeter – A voltmeter is vital, as I must make sure the potential difference remains constant throughout my investigation.
-
Ammeter – An ammeter is also vital, I examine the current and potential difference before I am able to determine the resistance.
-
Ruler – I must use a ruler to measure the length of the wires and make sure that it is accurate.
-
Crocodile Clips – Crocodile clips are required to connect all the wires, batteries, voltmeters and ammeters.
Number of Readings
In my investigation, I will repeat reading twice giving me a total of three readings. I believe this is suitable because it will be accurate but it is not too long and can be achieved in a very small period of time. I will also calculate the average. The table I propose to use is shown below.
I feel this is a good table of results because it is immensely easy to read from and it will contain a large amount of information.
Theory
The theory of Ohm’s Law is “The amount of current flowing in a circuit made up of pure resistances is directly proportional to the electromotive forces impressed on the circuit and inversely proportional to the total resistance of the circuit.”
Source: http://webhome.idirect.com/~jadams/electronics/ohm.html
Basically, Ohm’s Law means a steady increase in voltage, in a circuit with constant resistance, produces a constant linear rise in current. Secondly, A steady increase in resistance, in a circuit with constant voltage, produces a progressively weaker current. To show this in more detail, I found some more data, which gives me much more information.
Preliminary Work
At first glances, it seems that my prediction is indeed correct. However, this table cannot be used as concrete evidence as it has only one set of readings. I will carry out another test, this time with three readings. I will calculate the averages and this will be much more accurate.
You may notice that in this table it says 4v rather than the 2v I proposed to use. This is because when I set it on 2v, the current was very small and it was too difficult to read off the ammeter in the later stages of the experiment.
Results Table
Key
V = Potential Difference (measured in volts)
I = Current (measured in amps)
R = Resistance (measured in ohms) Formula = V/I = R
The two reading that are underlined were not used. I discarded them as they seemed unlikely and I wish to gain accurate results. These inaccurate results could have been caused by many factors. There could have been a lapse in my concentration and I might have placed the crocodile clip in the wrong place. However, this is only a possibility and it is impossible for me to say exactly what went wrong. The reason I made an error is not important
Analysis
The result table shows me that the length does indeed alter the resistance of a wire to a large degree.
The graph and table of results show us a pattern. We see that the longer the wire, the greater the resistance. The table below proves this.
The table above shows us that as the length of the wire doubles, the resistance of the wire approximately doubles. This proves my earlier statement that length is directly proportional to resistance. The reason my results are not that accurate is because I did not use a digital ammeter. I found the readings on the ammeter difficult to read and as the lowest reading on the ammeter was 0.2 amps so my last five results were all 0.2 amps, which I am sure, is not correct. If I was in possession of a digital ammeter, my readings will be clear and simple. Unfortunately,
none were available and my results were to some degree, inaccurate.
Evaluation
I thoroughly enjoyed this investigation. I also found it very easy and interesting. There were some aspects I did not understand when the task was first set but it all became clear when I started the investigation.
The accuracy of my investigation was not perfect. I did not have a digital ammeter or voltmeter, which meant it was difficult to read and it would have been less accurate. Also, looking at the ammeter and voltmeter from different angles would give different readings so this may have also affected my results. I can also place a lot of the blame on myself. Firstly I only repeated the test once. To increase accuracy, I could have repeated the test many times giving me a large number of results, which would certainly improve accuracy.
it appears to be a different reading and this would have made my results, to some degree, inaccurate.
